1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that includes a main pole and a shield.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system in which signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole allows a magnetic flux corresponding to the magnetic field produced by the coil to pass, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. The unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent the unwanted erasure.
A known technique for preventing the unwanted erasure induced by a skew is to configure the main pole so that its end face located in the medium facing surface decreases in width with increasing proximity to the top surface of the substrate, as described in U.S. Pat. No. 8,274,759 B1, for example. U.S. Pat. No. 8,274,759 B1 also describes a technique for configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface.
In order to prevent the unwanted erasure induced by a skew, it is also effective to reduce the thickness of the main pole in the medium facing surface. If the entire main pole is thinned, however, the main pole becomes small in cross-sectional area perpendicular to the direction in which magnetic flux flows. This makes it difficult for the main pole to guide much magnetic flux to the medium facing surface, thus leading to degradation of overwrite property.
Configuring the main pole so that its thickness in the vicinity of the medium facing surface decreases with increasing proximity to the medium facing surface as described in U.S. Pat. No. 8,274,759 B1 allows the main pole to have a small thickness in the medium facing surface and a large thickness in a portion away from the medium facing surface, thereby making it possible for the main pole to guide much magnetic flux to the medium facing surface.
Further, in order to prevent the unwanted erasure induced by a skew and achieve higher recording densities, it is effective to provide a write shield having an end face that is located in the medium facing surface at a position on the front side in the direction of travel of the recording medium relative to the end face of the main pole, as described in U.S. Pat. No. 8,274,759 B1.
A magnetic head having the write shield is typically provided with a return path section for connecting the write shield and part of the main pole located away from the medium facing surface to each other. The write shield, the return path section and the main pole define a space through which a coil portion passes. The write shield and the return path section have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, thereby preventing the magnetic flux from reaching the recording medium. The write shield and the return path section also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of an end of the end face of the main pole located in the medium facing surface, the end being located on the front side in the direction of travel of the recording medium. In order to define the position of the end of the record bit accurately, it is therefore important that the write shield have an end face that is located in the medium facing surface at a position on the front side in the direction of travel of the recording medium relative to the end face of the main pole and that this end face of the write shield capture a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium. The magnetic head having the write shield allows for prevention of the unwanted erasure and is able to provide a further improved recording density.
In view of the foregoing, in order to prevent the unwanted erasure induced by a skew and provide a higher recording density, the magnetic head can conceivably be configured so that a portion of the top surface of the main pole in the vicinity of the medium facing surface is formed into an inclined portion inclined relative to a direction perpendicular to the medium facing surface, and the write shield is provided with an inclined surface opposed to the inclined portion of the main pole.
In the above-described configuration, however, if the inclined portion of the top surface of the main pole and the inclined surface of the write shield are opposed to each other over a large area with a small spacing therebetween, there arises a problem that much magnetic flux leaks from the main pole to the write shield to cause degradation of write characteristics such as the overwrite property. To avoid this, at least one of the inclined portion and the inclined surface may be reduced in length in the direction perpendicular to the medium facing surface.
Reducing the inclined portion in length in the direction perpendicular to the medium facing surface, however, precludes a sufficient increase in the thickness of a portion of the main pole that is located farther from the medium facing surface than is the inclined portion. This causes the main pole to become unable to guide much magnetic flux to the medium facing surface, and thus leads to degradation of write characteristics such as the overwrite property.
On the other hand, reducing the inclined surface in length in the direction perpendicular to the medium facing surface causes a reduction in the volume of a portion of the write shield that is located on the front side in the direction of travel of the recording medium relative to the main pole, thereby compromising the function of the write shield. More specifically, the reduction in the volume of the aforementioned portion of the write shield is likely to cause the saturation of magnetic flux in that portion. This in turn causes leakage of magnetic flux from the portion toward the medium facing surface, thus raising a problem that the leakage flux may cause accidental erasure of data stored on the recording medium.
Thus, for the magnetic head including the write shield, it has conventionally been difficult to improve the write characteristics without compromising the function of the write shield.